Field of the Invention
The invention relates to a method for testing the tightness of a gas-containing specimen in a film chamber of a flexible material.
Description of Related Art
Film chambers are test chambers testing the tightness of specimens such as food packages or other flexible packages. Here, a film chamber is made at least in part of a soft flexible material which clings to the specimen in the film chamber when the film chamber is evacuated. A vacuum is generated inside the film chamber in the external environment of the specimen. This vacuum expels a filling gas contained in the specimen through possible leaks into the external environment of the specimen inside the film chamber. The atmospheric pressure outside the film chamber prevents the internal pressure of the specimen from causing the specimen to burst in the vacuum.
Conventionally, two alternative methods are known for testing the tightness of a specimen in a film chamber. In one method, a test gas is added to the filling gas in the specimen and the test gas partial pressure is measured in the gas flow of the vacuum system of the film chamber. Here, the test gas partial pressure serves as the measure for the leakage rate.
The other test method is independent of filling gas. In a first step the film chamber is evacuated and then a valve to the vacuum pump system is closed. Thereafter, in a second step, the pressure increase over time is measured inside the film chamber and outside the specimen. This pressure increase serves as a measure for the leakage rate of the specimen. Due to the two steps “evacuation” and “pressure measurement” that have to be performed one after the other, this method is disadvantageous for industrial tightness tests, since these require short cycle rates in tightness testing. It is another disadvantage that in case of a large leakage of the specimen the filling gas will be pumped out from the specimen already during the evacuation phase. Thus, after evacuation, the specimen is also evacuated and will erroneously be considered tight during the pressure measurement phase.
It is an object of the invention to provide an improved method for testing the tightness of a specimen in a film chamber.